In order to detect anomalies in the formation of through-holes (hereinafter, throughout this specification, the term “through-hole” means a set of a through-hole and a conductive material formed within the through-hole) etc., during the manufacture of semiconductor device, a check pattern, separate from a real device, for detecting defects created in the through holes is formed on individual chips on a wafer and then is measured as to what resistance the through-holes have to identify the presence or absence of defects in the through-holes and the locations thereof.
FIG. 5 is a schematic diagram showing a conventional scanning probe inspection apparatus (called a scan type probe microscope too) for detection of anomalies in the formation of through-holes. A plurality of through-holes 2 are arranged at equal intervals between a pair of pads 1 having dimensions on the order of 100.times.100 μm and formed on an insulating layer on the top surface of a substrate. Furthermore, those through-holes are connected to upper and lower interconnect lines such that except for the upper interconnect lines directly coupled to the pads 1, one upper interconnect line is coupled to an upper end of one through-hole out of adjacent through-holes and one lower interconnect line partially facing the one upper interconnect line is coupled to a lower end of one through-hole out of adjacent through-holes, and the one lower interconnect line is coupled to a lower end of the other through-hole out of adjacent through-holes, thereby forming a chain unit, and further, a plurality of chain units are coupled to one another in series to form a chain pattern (check pattern). In this case, the lower interconnect lines are embedded in the insulating film on the surface of the substrate. Thus, a chain-like check pattern is formed in which the plurality of through-holes 2 are connected in series through the upper and lower interconnect lines 4, 3 and the pads 1 are connected to both ends of the check pattern. It should be noted that the check pattern generally includes a significantly large number (in the figure, only eight pieces of through-holes are illustrated for simplification) of through-holes, for example, 10,000 pieces of through-holes. In this case, a chain unit consisting of a pair of through-holes 2, a lower interconnect line 3 coupling together the pair of through-holes 2, and an upper interconnect line 4 coupled to an upper end of one of the pair of through-holes 2 is repeatedly formed to construct chain units that have a pitch of typically not greater than 1 μm. The individual through-holes are normally formed to have a resistance of about 1 ohm and therefore, the check pattern (including 10,000 through-holes) is formed to have the designed resistance, i.e., 10 kilo-ohms between both ends of the pattern.
In the conventional scanning probe inspection apparatus, a DC power supply 5 (for supplying a DC voltage V0) is connected between one pad 1 (hereinafter called a reference pad) out of a pair of pads and a conductive probe 6, and then, the probe 6 operates so that the probe 6 begins moving from the upper interconnect line 4 on the side of the reference pad 1 to which the supply is connected and continue moving over the surface of a substrate in a sliding fashion in a direction in which the probe is apart from the reference pad 1. During scanning of the probe 6, current I flowing through a detection circuit constituted by the probe 6 and the DC power supply connected to the probe is measured. In this case, during movement of the probe 6, predetermined current is detected while the probe 6 is in contact with the upper interconnect line 4 and no current is detected while the probe 6 is sliding on the surface of the insulating layer on the substrate because the detection circuit is open. Therefore, the current I flowing through the detection circuit changes pulsewise as the probe moves. As the probe 6 moves away from the reference pad 1, the number of the through holes 2 between the probe 6 and the reference pad 1 increases, and the resistance therebetween thus increases, causing the current I flowing through the detection circuit to become smaller. As mentioned above, the resistance of one through hole 2 is normally about 1 ohm. Therefore, all the series-connected 10,000 through-holes included in the detection circuit have an overall resistance, 10 kilo-ohms, i.e., the resistance of the check pattern when the probe 6 is positioned farthest from the reference pad 1. At this point, assume that the check pattern that has a resistance of 10 kilo-ohms when the pattern contains no defective through-hole is measured as having a resistance of 20 kilo-ohms. In this case, two events are considered to have occurred. That is, the individual through-holes are uniformly formed to have a resistance of 2 ohms and any one of the through-holes is formed defective to have a resistance of 10 kilo-ohms, which is added to the resistance of other normal through-holes. In the former case, all the through holes are defective, eliminating necessity of identification of defective through-hole. In the latter case, when the probe 6 is moved and located on the upper interconnect line 4 that is connected to this defective through-hole 2, the resistance measured becomes enlarged while current measured largely decreases. Accordingly, detecting enlargement of the resistance allows identification of defective through-hole. Note that the check pattern actually is formed to have a plurality of arrangements of through-holes connected together in rows and the probe scans over the plurality of arrangements of through-holes two-dimensionally. After identification of the defective through-hole, the corresponding portion is cut and the cross section of the portion is observed by a transmission electron microscopy or the like, and an anomaly in the profile of the cross section is detected to determine what causes the defect. The results obtained by the detection are fed back to the fabrication process for a semiconductor device to suppress the occurrence of defects.
A conventional scanning probe microscope has been proposed in which two or more electrically independent probes are constituted by carbon nano tubes and scan minute materials of not greater than 100 nm, allowing measurement of electrical characteristics (Japanese Patent Laid-Open No. 2002-214112).
Further, as a method of detecting anomalies in the formation of through-holes, a scheme called OBIRCH (Optical Beam Induced Resistance Change) is proposed. According to this scheme, a laser beam scans over and is irradiated onto a through hole pattern, and heat from the laser beam is absorbed by a void at the location of a defective through-hole, and then, change in current is detected, allowing identification of the defective through-hole.
However, the conventional techniques include the following problems. That is, in a case where the resistance of a defective through-hole is high, it is possible to detect and identify the defective through-hole. However, in a case where the resistance thereof is low, it is not possible to detect the defective through-hole, meaning that the sensitivity with which the defective through-hole is detected is low. There exists a contact resistance between the probe 6 and the upper interconnect line 4. Therefore, while the probe 6 scans, fluctuation of the current detected, due to change in contact resistance, is observed.
As such, in a case where the resistance of the defective through-hole is low, even when the probe reaches the location of the defective through-hole and the current detected changes stepwise, this change is not detectable due to variations in contact resistance and whether the through-hole is defective cannot be detected.
The contact resistance is typically as large as over 1 kilo-ohms and when the resistance of a defective through-hole is relatively low, e. g., 10 ohms to 1 kilo-ohms, the defective through-hole cannot be detected due to change (variations) in contact resistance during probe scanning.
The method described in Japanese Patent Laid-Open No. 2002-214112 needs to use a carbon nano tube and has a shortcoming of having high cost of detection. Furthermore, the diameter of laser beam is greater than that of through-hole in the OBIRCH scheme and therefore, a defective through-hole cannot be identified.